This invention relates to spectrophotometry and the spectrophotometric analysis of blood samples. In particular, this invention relates to a method and apparatus for providing a rapid pre-test determination of interferent concentration, specimen type and physical properties of a blood sample for a blood analyzer by measurement of absorbance or reflectance.
Clinical laboratory tests are routinely performed on the serum or plasma of whole blood. In a routine assay, red blood cells are separated from plasma by centrifugation, or red blood cells and various plasma proteins are separated from serum by dotting prior to centrifugation.
Haemoglobin (Hb), bilirubin (Bili) and light-scattering substances like lipid particles are typical substances which will interfere with, and affect spectrophotometric and other blood analytical measurements. Such substances are referred to as interferents.
Many tests conducted on plasma or serum samples employ a series of reactions which terminate after the generation of chromophores which facilitate detection by spectrophotometric measurements at one or two wavelengths. Measurement of interfering substances prior to conducting such tests is important in providing meaningful and accurate test results. In fact if a sample is sufficiently contaminated with interferents, tests are normally not conducted as the results will not be reliable.
In analytical laboratories bar codes are increasingly being used to identify samples, and such laboratories routinely analyze a variety of biologic fluids, for example, the most common being blood and urine.
Specimen integrity directly affects the accuracy of test results. Numerous factors can compromise specimen integrity such as, having the right sample, e.g., blood rather than urine; in the case of a blood sample, whether it is serum or plasma; the presence of interferents in a plasma or serum sample; the volume of the sample; the sample temperature; and the location of the upper surface of a gel barrier, which is also referred to herein as the gel level, in a blood sample, where the gel is an inert material used to separate serum or plasma from clotted or packed blood bells, respectively. Finally, it is critical that the sample tested be properly matched to the results of any assessments on the sample.
Current methods used for quality assurance and specimen integrity rely principally on visual inspection of the specimen with or without comparison to a reference chart, depending upon which variable is being assessed. Visual inspection of samples is sometimes employed on a retrospective basis where there is disagreement between test results and clinical status of the patient in order to help explain such discrepancies.
A sample of plasma or serum is normally transferred from the original tube to a secondary tube. These secondary tubes may be amber coloured to protect photo sensitive constituents. Amber colouring makes visual inspection virtually impossible. On occasion, labels cover portions of the tube further restricting a full visual examination. Further, it is sometimes difficult to distinguish between urine and plasma or serum samples, even in transparent tubes.
Pre-test screening of specimens by visual inspection is semi-quantitative at best, and highly subjective and may not provide the quality assurance required.
Furthermore, visual inspection of specimens is a time consuming, rate limiting process. Consequently, state-of-the-art blood analyzers in fully and semi-automated laboratories do not employ visual inspection of specimens. However, other methods such as direct sampling are not rapid enough or cost effective. In order to obtain a measurement of the sample of the plasma or serum, specimen tubes must be uncapped, a direct sample of the specimen taken and diluted prior to measurement.
The disadvantages of the prior art may be overcome by providing a rapid and accurate method and apparatus for monitoring blood specimens before samples are presented for analysis.
In one aspect of the invention, the bar code on the specimen tube is read to identify the specimen, as well as the bar code reading, determination of the gel level of the specimen and the height of fluid above the gel provide the basis for positioning the specimen container so that spectral data can be obtained. The spectral data is used in a novel way to determine if the specimen which is presented for analysis contains interferents and if so, to what extent; to determine specimen type, for example if it is urine or plasma or serum; and to determine the temperature of the specimen.
In another aspect of the invention, there is provided an apparatus which incorporates: A. a device to read any bar code present on a specimen container and thereby identify and provide information with respect to positioning the specimen; B. a device to determine the location of the upper surface of a gel barrier of the specimen and the height of fluid above the gel; and C. A spectrophotometric device to irradiate and measure radiation from the specimen so as to determine if the specimen which is presented for analysis contains interferents and if so, to what extent; to determine specimen type; and to determine the temperature of the specimen. This apparatus is capable of these determinations where the sample tube containing the specimen has a sample identification label on the exterior surface.
In a further aspect of the invention, there is provided a method for the following: to read any bar code present on specimen container and thereby identify and provide information with respect to positioning the specimen; to determine the location of the upper surface of a gel barrier of the specimen and the height of fluid above the gel; to determine if the specimen which is presented for analysis contains interferents and if so, to what extent; to determine specimen type; and to determine the temperature of the specimen. The method of this invention allows for these determinations where the sample tube containing the specimen has a sample identification label on the exterior surface.
In yet another aspect of the invention, there is provided an apparatus and a method for the determinations described herein where the radiation from the spectrophotometer, or other appropriate source, is transmitted through the label, container and specimen.
In one embodiment, the bar code reading as well as the gel level and height of fluid above the gel are first determined. This determination provides information essential for proper positioning of the sample for the following determinations. The concentration of interferents such as hemoglobin (Hb), total bilirubin (calibrated for unconjugated bilirubin, conjugated bilirubin, delta bilirubin, the sum of results for these three gives total bilirubin) and lipids are determined by measurement of absorption of different wavelengths of light in serum or plasma specimens which are then compared with values obtained through calibration using reference measurements for the respective interferents in serum or plasma specimens. This is true also for determination of temperature of the sample. A determination of specimen type, for example whether the specimen is urine or plasma or serum, is also made. This determination is made by recordal of spectral data for different samples then through statistical analysis, the spectra are classified according to sample type. In addition a bar code reading is carried out either simultaneously, before or after the determination of the other parameters. To those skilled in the art, it is clear that although certain sequences of determinations are outlined here, any combination or sequence of combinations is within the scope of this invention.
In another embodiment, the bar code reading as well as the gel level and height of fluid above the gel are first determined. This determination provides information essential for proper positioning of the sample for the following determinations. The concentration of interferents such as hemoglobin (Hb), total bilirubin (calibrated for unconjugated bilirubin, conjugated bilirubin, and delta bilirubin, the sum of results for these three gives total bilirubin) and lipids are determined by measurement of reflectance of different wavelengths of light in serum or plasma specimens which are then compared with values obtained through calibration using reference measurements for the respective interferents in serum of plasma specimens. This is true also for determination of temperature of the sample. A determination of specimen type, for example whether the specimen is urine or plasma or serum, is also made. This determination is made by recordal of spectral data for different samples then through statistical analysis, the spectra are classified according to sample type. In addition a bar code reading is carried out either simultaneously, before or after the determination of the other parameters. To those skilled in the art, it is clear that although certain sequences of determinations are outlined here, any combination or sequence of combinations is within the scope of this invention.